The couple lives together in London and Waterhouse said that they make efforts to see each other during their busy schedules, like her recent tour.
Her interviewer, Laura Pullman, noted that the longest they've spent apart is two months.
"I had two days off the other day, and it was like, no question I'm going back to see him," she said. "Then he'll come out for a couple of days."
"I'm shocked that I'm so happy with someone for nearly five years," Waterhouse said of her relationship.
Even though they're both actors, Waterhouse said that "Rob definitely isn't getting advice from me about acting, but of course I'll try and get him to help me with an audition before he falls asleep on the sofa."
Waterhouse also said that she and Pattinson maintain a mutual joy about each other.
"I'm always incredibly excited when I see his name pop up [on my phone] or even a text, and I think he feels the same about me," she said. "We've always got so much to say, and I find him hilarious."
She also spoke about both of them growing up in separate parts of England.
"We always say that I never, ever would have thought I'd go out with a boy from Barnes, and he didn't think he'd go out with a girl from Chiswick," Waterhouse said.